Reduction of metal oxides using gas stream containing both hydrocarbon and hydrogen

ABSTRACT

A gas stream containing both hydrocarbon and hydrogen is separated into a hydrogen-rich fraction and a hydrocarbon-rich fraction. Then at least one sub-quantity of the hydrocarbon-rich fraction is subjected to at least one operation from the group oxidation using technically pure oxygen and reforming using CO 2  and H 2 O. The result is introduced at least as a component of a reduction gas into a reduction unit containing the metal oxides. As a result of the at least one operation, the hydrocarbon content in the reduction gas on entry into the reduction unit is below 12% by volume.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the U.S. national stage of International ApplicationNo. PCT/EP2012/054863, filed Mar. 7, 2012 and claims the benefitthereof. The International Application claims the benefit of AustrianApplication No. A785/2011 filed on May 30, 2011, both applications areincorporated by reference herein in their entirety.

BACKGROUND

Described below are a process for reducing metal oxides, such as ironoxides, using a gas stream containing both hydrocarbon and hydrogen anda device for carrying out such a process.

Coke oven gas is formed when coke is generated in integrated smeltingworks or stand-alone production plants and is used to date, for example,for reinforcing the heating value of the blast furnace top gases beforeuse thereof in recuperators, as fuel gas in slab reheating furnaces orroller hearth furnaces, and for electricity generation in power plants.As main components it contains not only hydrocarbon—for example one ormore hydrocarbons C_(n)H_(2n+2), wherein n can be 1 or 2 or 3 or 4; butchiefly methane, that is to say n=1—but also hydrogen. In someintegrated smelting works, coke oven gas is also used for generatingtechnically pure hydrogen, for example for use in annealing furnaces.Typical coke oven gas compositions formed in integrated smelting worksare as follows

COG analysis (dry): H₂ [% by volume] 65 62.1 N₂ [% by volume] 2.5Included in remainder CO [% by volume] 6 6.2 CH₄ [% by volume] 22 21.4C_(n)H_(m) [% by volume] 3 Included in remainder CO₂ [% by volume] 1.5Included in remainder H₂O [% by volume] Saturated Included in remainderH₂S [g/Nm³ (S.T.P)] 0.35 n.a. Tar [g/Nm³ (S.T.P)] 5 n.a. Dust [g/Nm³(S.T.P)] 5 n.a. Remainder [% by volume] — 10.3

Although the coke oven gas contains components such as hydrogen andcarbon monoxide which are readily usable for reducing metal oxides ingeneral, and iron oxides in particular, on account of the hydrocarboncontent, it can only be used with restrictions for reducing metaloxides, especially iron oxides, in a reducing unit, since, as aconsequence of highly endothermic reactions of the hydrocarbonsproceeding on the introduction of coke oven gas into the reducing unit,for example hydrocarbon CH₄

CH₄→2H₂+C Cracking ΔH₂₉₈=+74.86[kJ/mol]

3Fe+CH₄→Fe₃C+2H₂ Carbonizing ΔH₂₉₈=+99.7[kJ/mol]

the reduction temperature would decrease too greatly, which in turnwould greatly restrict the productivity of the reducing unit.

SUMMARY

Described below are a process which permits the use of a gas streamcontaining hydrocarbon and hydrogen for reducing metal oxides and adevice for carrying out such a process.

This process for reducing metal oxides uses a gas stream containing notonly hydrocarbon but also hydrogen, which is characterized in that thegas stream containing not only hydrocarbon but also hydrogen isseparated into a hydrogen-rich fraction and a hydrocarbon-rich fraction,and subsequently at least a subquantity of the hydrocarbon-rich fractionis subjected to at least one operation of the group

-   oxidation using technically pure oxygen,-   reformation using CO₂ and H₂O,    and then it is introduced at least as a component of a reducing gas    into a reducing unit containing the metal oxides, wherein the    hydrocarbon content is adjusted by the at least one operation of the    aforementioned group, in such a manner that the hydrocarbon content    in the reducing gas is, on entry into the reducing unit, less than    12% by volume, such as less than 10% by volume, particularly less    than 8% by volume.

Metal oxides can be, for example, iron oxides, or oxides of nickel,copper, lead, cobalt.

The reduction of the metal oxides proceeds to form extensively metalizedmetal—that is to say the degree of metalization is greater than or equalto 90%, which may be greater than or equal to 92%, for example spongeiron.

The gas stream containing not only hydrocarbon but also hydrogen cancontain one or two or more types of hydrocarbon.

For example, it contains relatively low-saturated hydrocarbonsC_(n)H_(2n+2), wherein n=1, that is to say methane, or n=2, that is tosay ethane, or n=3, that is to say propane, or n=4, that is to saybutane or isobutane. It can also contain relatively low-monounsaturatedor polyunsaturated hydrocarbons, wherein, for example, C_(n)H_(2n)applies, for example ethene. It can also contain aromatic hydrocarbons,such as benzene or toluene. In the gas stream containing not onlyhydrocarbon but also hydrogen, one or more types of hydrocarbon havingthe general formula C_(n)H_(m) can also be present, wherein m can be

m=n,

m=2n,

m=2n+2.

The gas stream containing not only hydrocarbon but also hydrogen isseparated into a hydrogen-rich fraction and a hydrocarbon-rich fraction.In this case the hydrocarbon-rich fraction contains not onlyhydrocarbons, but also further components such as argon, nitrogen,carbon monoxide, carbon dioxide and steam. The term hydrocarbon-richrelates to the fact that this fraction, compared with the gas streamcontaining not only hydrocarbon but also hydrogen, has a higher contentof hydrocarbon. \

The hydrogen-rich fraction contains not only hydrogen.

The term hydrogen-rich relates to the fact that this fraction, comparedwith the gas stream containing not only hydrocarbon but also hydrogen,has a higher content of hydrogen.

Subsequently for the separation, at least a subquantity of thehydrocarbon-rich fraction obtained in the separation is subjected to atleast one operation of the group

-   oxidation using technically pure oxygen,-   reforming using CO₂ and H₂O.

It can also be subjected to a combination of these two operations.

In the case of a combination, partial oxidation may be performed firstusing technically pure oxygen for the purpose of temperature elevation,and subsequently reforming is performed using CO₂ and H₂O, for examplein an autothermal reformer. In an autothermal reformer, the reformerdoes not need to be fired, because no feed line of fuel gas to theautothermal reformer is necessary. This saves expenditure onconstruction and reduces the exhaust gases of the reformer.

In this case, in the oxidation, the total amount of hydrocarbons is notoxidized, but only a part of the amount of hydrocarbons—in the contextof this application, this is also termed partial oxidation.

In this case, in the reforming, the total amount of hydrocarbons is notreformed, but a predominant part of the amount of hydrocarbons.

Via the operations described, alone or in combination, the content ofhydrocarbons decreases.

After at least a subquantity of the hydrocarbon-rich fraction obtainedin the separation has been subjected to at least one operation of thegroup, it is introduced at least as a component of a reducing gas into areducing unit containing the metal oxides—this means of course that theproduct obtained in the operation or operations is introduced.

At least as a component of a reducing gas means that the reducing gascan also contain other components which may optionally be added before amixture obtained in the addition is introduced as reducing gas into thereducing unit.

As described below, the hydrocarbon content of the subquantity is set bythe at least one operation of the group in such a manner that thehydrocarbon content in the reducing gas, on entry into the reducingunit, is less than 12% by volume, such as less than 10% by volume,particularly less than 8% by volume, but greater than 1% by volume,desirably greater than 2% by volume, particularly desirably greater than3% by volume. These limits are included herein. The higher thehydrocarbon content is in the reducing gas on entry into the reducingunit, the higher the reduction temperature must be set—in reducingshafts as reducing unit, also termed—gas temperature bustle or the loweris the productivity of the plant. At a set hydrocarbon content, thereduction temperature owing to a lower endothermic reactions of thehydrocarbons does not fall so greatly that the productivity of thereducing unit decreases below an economically acceptable level.

The lower limit of the hydrocarbon content is determined, for example,in the reduction of iron oxides, by the required carbon content—carbonbound as Fe₃C or elemental carbon—in the reduced product for thesteelworks—there, for example, an electric arc furnace. With increasingcarbon content in the reduced product, the energy requirement in thesubsequent treatment in the electric arc furnace decreases. Ahydrocarbon content in the reducing gas on entry into the reducing unitin the range of the lower limit is used, for example, for generating aminimum content of carbon in a sponge iron, in particular in the form ofFe₃C, or such a hydrocarbon content is necessary optionally forcontrolling the temperature in the reducing unit.

In addition, for example in the production of sponge iron, hotbriquetted iron (HBI) plants—as are customary in direct reduction (DR)plants—also require certain minimum briquettingtemperatures—desirably >650° C. for avoidance of increased maintenancecosts and to achieve product densities >5 g/cm³—which, in the event ofexcessive cooling of the DRI in the reducing unit, cannot be achievedowing to endothermal reactions.

According to an embodiment, the gas stream containing not onlyhydrocarbon but also hydrogen is coke oven gas.

The latter embodiment is desirable because coke oven gas, in anintegrated smelting works, is usually formed in any case, or, in astand-alone coking plant, is only used for electricity generation, or isflared off without being used. Using the process, it can be utilized forefficient iron production; the material utilization thereof achieved inthis case has a higher efficiency than, for example, utilization forelectricity generation. An integrated smelting works is taken to mean asteel generation route which consists, inter alia, of coking plant,sintering plant and blast furnace. The gas stream containing not onlyhydrocarbon but also hydrogen can also be gas generated in a coalgasifier.

According to an embodiment, the gas stream containing not onlyhydrocarbon but also hydrogen is separated into a hydrogen-rich fractionand a hydrocarbon-rich fraction by at least one operation of the group

-   pressure-swing adsorption,-   membrane separation.

The pressure-swing adsorption proceeds, for example, in a PSA or VPSAplant, wherein PSA means Pressure Swing Adsorption and VPSA means VacuumPressure Swing Adsorption. More desirably, a prepurification of the gasstream proceeds before the pressure-swing adsorption, for example in aprepurification appliance for separating off tar and dust using tarfilters made of fibers or adsorption materials. Owing to the differingadsorption forces, a gas stream containing not only hydrocarbon but alsohydrogen, for example coke oven gas, in the case of an appropriatedesign of the plant size of pressure-swing adsorption plants and byoperation using correspondingly designed cycle times using a PSA plantor a VPSA plant can be separated into a hydrogen-rich fraction and ahydrocarbon-rich fraction. The hydrogen is formed on the product sidevirtually without a significant pressure drop. The hydrocarbon-richfraction is formed at very low pressure or a vacuum and is thencompressed to the required pressure subsequently in the process.

In the case of membrane separation, the separation proceeds on the basisof the differing permeability of a membrane. Hydrogen is produced inthis case in the concentrated state on the low-pressure side of themembrane.

According to an embodiment, at least a proportion of the at least onesubquantity of the hydrocarbon-rich fraction which was subjected to atleast one operation of the group

-   oxidation using technically pure oxygen,-   reforming using CO₂ and H₂O, is mixed with an auxiliary reducing    gas, before the resultant mixture of these two components is    introduced as reducing gas into the reducing unit containing the    metal oxides.

In this case the reducing gas introduced into the reducing unitcontaining the metal oxides is generated by mixing two components,wherein the one component is obtained by oxidizing and/or reforming atleast one subquantity of the hydrocarbon-rich fraction.

In such a procedure, other gases having a reduction potential can alsobe materially utilized for the reduction of metal oxides by adding themas auxiliary reducing gas.

In a device for carrying out the process, corresponding feed lines arepresent for introducing auxiliary reducing gases to the proportion ofthe hydrocarbon-rich fraction, or optionally to the total amount of thehydrocarbon-rich fraction, which has been subjected to at least oneoperation of the group

-   oxidation using technically pure oxygen,-   reforming using CO₂ and H₂O.

According to an embodiment, the mixing ratio of the two components isset in dependence on a preset temperature for the mixture. In thismanner, it is ensured that the reducing gas is in the temperature regionwhich is favorable in terms of the process and economics for reducingmetal oxides. By setting the temperature, the reaction rate in thereducing reactor—kinetics, can be set optimally. In addition, theefficiency of the reducing gas preheating can be optimized.

Corresponding devices for controlling the mixing ratio and alsotemperature measuring devices for measuring the temperature of themixture and/or for measuring the temperatures of the components arepresent in a device for carrying out the process.

According to an embodiment, the two components are mixed after theauxiliary reducing gas has been heated in a gas furnace. This makespossible an improved temperature setting of the reducing gas. Thetemperature of the reducing gas may be in the range 780-1050° C.,according to the H₂/CO ratio in the reducing gas.

According to an embodiment, top gas is taken off from the reducing unit,and the auxiliary reducing gas is obtained at least in part by mixingtop gas that is dedusted and substantially freed from CO₂, and at leastone further gas. In this manner, the reductants (CO and H₂) stillpresent in the top gas are utilized again for reducing the metal oxides.

Advantageously, the at least one further gas includes the hydrogen-richfraction obtained in the separation of the gas stream, such as coke ovengas, containing not only hydrocarbon but also hydrogen.

In this manner, the reduction potential present in this fraction is alsoutilized for reducing metal oxide; utilized, especially in that thereduction rate—kinetics—is generally more rapid via hydrogen:

3Fe₂O₃+H₂→2Fe₃O₄+H₂O ΔH₂₉₈=−2.72 [kJ/mol]

Fe₃O₄+H₂→3FeO+H₂O ΔH₂₉₈=+59.83 [kJ/mol]

FeO+3H₂→Fe+2H₂+H₂O ΔH₂₉₈=+29.60 [kJ/mol]

Advantageously, the gas furnace is operated with a fuel gas which atleast in part includes at least one gas of the group

-   tail gas formed in the removal of CO₂ from the top gas,-   top gas,-   gas stream, such as coke oven gas, containing not only hydrocarbon    but also hydrogen,-   hydrogen-rich fraction obtained by separation of the gas stream,    such as coke oven gas, containing not only hydrocarbon but also    hydrogen,-   hydrocarbon-rich fraction obtained by separation of the gas stream,    such as coke oven gas, containing not only hydrocarbon but also    hydrogen.

In this manner, these gases are utilized in the process for reducingmetal oxides, which increases the efficiency thereof. When hydrogen-richgases are used for firing the gas furnace from below, the CO₂ emissioncan be kept correspondingly low.

Single, a plurality of, or all of the corresponding fuel gas feedline(s) to the gas furnace is/are present in a device for carrying outthe process:

-   a tail gas feed line for feeding tail gas produced in the removal of    CO₂ from the top gas, which tail gas feed line exits from the CO₂    removal plant.-   A top gas feed line for feeding top gas, which top gas feed line    exits from a top gas outlet line withdrawing top gas from the    reducing unit.-   A fuel gas feed line for feeding gas stream containing not only    hydrocarbon but also hydrogen, which fuel gas feed line exits from a    feed line for a gas stream containing not only hydrocarbon but also    hydrogen and which itself opens out into a device for separating a    gas stream containing not only hydrocarbon but also hydrogen into a    hydrogen-rich fraction and a hydrocarbon-rich fraction.-   A fuel gas feed line for feeding a hydrogen-rich fraction obtained    by separation of the gas stream, such as coke oven gas, containing    not only hydrocarbon but also hydrogen, which fuel gas feed line    exits from a device for separating a gas stream containing not only    hydrocarbon but also hydrogen into a hydrogen-rich fraction and a    hydrocarbon-rich fraction, or from an outlet line for the    hydrogen-rich fraction which itself arises from a device for    separating a gas stream containing not only hydrocarbon but also    hydrogen into a hydrogen-rich fraction and a hydrocarbon-rich    fraction,-   a fuel gas feed line for feeding a hydrocarbon-rich, hydrogen-rich    fraction obtained by separation of the gas stream, such as coke oven    gas, containing not only hydrocarbon but also hydrogen, which fuel    gas feed line exits from a feed line for the hydrocarbon-rich,    hydrogen-rich fraction which itself arises from a device for    separating a gas stream containing not only hydrocarbon but also    hydrogen into a hydrogen-rich fraction and a hydrocarbon-rich    fraction, or a device for separating a gas stream containing not    only hydrocarbon but also hydrogen into a hydrogen-rich fraction and    a hydrocarbon-rich fraction.

Advantageously, the reducing unit is a reducing shaft and a firstsubquantity of the hydrocarbon-rich fraction is introduced directly intothe reducing shaft, and a second subquantity of the hydrocarbon-richfraction before introduction thereof into the reducing shaft issubjected to at least one operation of the group

-   oxidation using technically pure oxygen-   reforming using CO₂ and H₂O, and then is introduced at least as    component of a reducing gas into a reducing unit containing the    metal oxides, and the hydrocarbon content is set by the at least one    operation of the group, in such a manner that the hydrocarbon    content in the reducing gas, on entry into the reducing unit, is    less than 12% by volume, such as less than 10% by volume,    particularly less than 8% by volume.

The first subquantity can thus be utilized for carbonization of themetal generated in the reducing unit; for example, it can be utilizedfor carbonization of metallic iron.

Advantageously, the at least one gas stream containing CO₂ and/or H₂O isadded to the hydrocarbon-rich fraction before reforming using CO₂ andH₂O. In this process, this can be, for example, steam, tail gas from aCO₂ removal process—for example from the removal of CO₂ from the topgas—top gas from the reducing shaft, or converter gas. Water can also beadded.

In this manner, these gases are utilized in the process for reducingmetal oxides, which increases the efficiency thereof, and reduces theenvironmental emissions, since CO₂ is converted back to CO.

Corresponding feed lines for feeding one or more of these gases whichexit from devices producing such gases or lines bearing such gases arepresent in a device for carrying out the process.

In the hydrocarbon-rich fraction, H₂S is also enriched. According to anembodiment, therefore, desulfurization of the hydrocarbon-rich fractionis carried out before it is subjected to at least one operation of thegroup

-   oxidation with technically pure oxygen,-   reforming using CO₂ and H₂O or.

The sulfur content can thereby be reduced in the largely metalizedmetal.

In a device for carrying out the process, then, in a feed line for thehydrocarbon-rich fraction 3, a desulfurization device is present,before—seen in the direction of flow—the feed line opens out into a unitfor carrying out an operation of the group

-   oxidation with technically pure oxygen,-   reforming using CO₂ and H₂O.

The process has the following advantages:

-   efficient material utilization of coke oven gas for reducing metal    oxides, especially for reducing iron oxides for sponge iron    production—advantage in comparison with the thermal utilization of    coke oven gas proceeding to date according to the related art,-   in comparison with utilization of natural gas for reducing metal    oxides, especially for the reduction of iron oxides for sponge iron    production, high economic advantages in comparison with natural gas,    since the coke oven gas is produced at lower costs-   very environmentally friendly process, in particular owing to low    CO₂ and NO_(x) emissions, since firstly in some embodiments a very    hydrogen-rich gas can be used for the reduction and secondly by    utilization of low-carbon gases in the reformer and/or gas furnace,    emissions thereof can further be reduced.-   Furthermore, in the reformer, some of the CO₂ emissions can be    converted back to CO and subsequently utilized for the reduction.

The specific carbon emission factor in the case of coke oven gas is 43.7kg of CO₂/GJ of fuel, while in the case of natural gas it is 55.7 kg ofCO₂/GJ of fuel. The use of coke oven gas is therefore considerably moreenvironmentally friendly than the use of natural gas.

A further subject matter of the present application is a device forcarrying out the process having a reducing unit for reducing metaloxides, having a device for separating a gas stream containing not onlyhydrocarbon but also hydrogen into a hydrogen-rich fraction and ahydrocarbon-rich fraction, having, arising therefrom, a feed line forthe hydrocarbon-rich fraction which opens out into a unit for carryingout an operation of the group

-   oxidation using technically pure oxygen-   reforming using CO₂ and H₂O, and having one or more introduction    lines for introducing at least one gas stream from the group-   hydrocarbon-rich fraction,-   gas stream obtained in the unit for carrying out oxidation using    technically pure oxygen,-   gas stream obtained in the unit for carrying out reforming using CO₂    and H₂O, into the reducing unit.

The device for separating a gas stream containing not only hydrocarbonbut also hydrogen into a hydrogen-rich fraction and a hydrocarbon-richhydrogen-rich fraction may be a device for separating coke oven gas intoa hydrogen-rich fraction and a hydrocarbon-rich fraction.

The device for separating a gas stream containing not only hydrocarbonbut also hydrogen into a hydrogen-rich fraction and a hydrocarbon-richfraction may be a device of the group

-   device for pressure-swing adsorption,-   device for membrane separation.

The one or more introduction lines may open out into the reducing unit,wherein upstream of the opening of at least one of the introductionlines into the reducing unit, an auxiliary reducing gas line for feedingauxiliary reducing gas to the reducing unit opens out into thisintroduction line.

Upstream of the opening of the auxiliary reducing gas line into theintroduction line, a gas furnace may be present in the auxiliaryreducing gas line.

Desirably, x introduction lines are present, wherein x is greater than 2or is equal to 2, of the at most x−1 introduction lines it is true that,upstream of the opening of at least one of the introduction lines intothe reducing unit, an auxiliary reducing gas line, for feeding auxiliaryreducing gas to the reducing unit, opens out into this introductionline.

In this manner, at least one introduction line is present into which noauxiliary reducing gas line opens out. Therefore, a subquantity of thehydrocarbon-rich fraction can be introduced directly into the reducingshaft without being mixed with auxiliary reducing gas; this subquantitycan be used, for example, for carbonizing the metal generated in thereducing unit; for example it can be used for carbonizing metallic iron.

According to one embodiment, the reducing unit is a reducing shaft, forexample a fixed-bed reducing shaft for carrying out a MIDREX® or HYL®reduction process.

According to one embodiment, the reducing unit is a fluidized-bedcascade.

An exemplary embodiment will be described in detail with reference to adrawing. In the drawings:

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects and advantages will become more apparent andmore readily appreciated from the following description of the exemplaryembodiments, taken in conjunction with the schematic and exemplarydrawings of which:

FIG. 1 is block diagram of a device for carrying out a process in whichcoke oven gas is separated into a hydrogen-rich fraction and ahydrocarbon-rich fraction and the latter is subjected to an oxidationbefore it is introduced into a reducing shaft as part of a reducing gas.

FIG. 2 is block diagram of a device and procedure similar to FIG. 1,with the difference that the hydrocarbon-rich fraction is subjected toreforming using CO₂ and H₂O before it is introduced as part of areducing gas into a reducing shaft.

FIG. 3 is block diagram of a device and procedure which chiefly differsfrom FIG. 1 in that a fluidized-bed cascade is present as reducing unit,and the device present for separating coke oven gas, instead of a devicefor pressure-swing adsorption, is a device for membrane separation.

FIG. 4 is block diagram of a device and procedure which chiefly differsfrom FIG. 1 in that a fluidized-bed cascade is present as reducing unit,and the device for separating coke oven gas, instead of a device forpressure-swing adsorption, is a device for membrane separation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Reference will now be made in detail to the preferred embodiments,examples of which are illustrated in the accompanying drawings, whereinlike reference numerals refer to like elements throughout.

FIG. 1 shows a device for carrying out a process. This includes, as areducing unit for reducing metal oxides, a reducing shaft 1 whichcontains iron ore, that is to say iron oxides. It likewise includes adevice for separating a gas stream containing not only hydrocarbon butalso hydrogen, in this case a PSA or a VPSA plant 2 using pressure-swingadsorption, into a hydrogen-rich fraction and a hydrocarbon-richfraction. In the present example, the gas stream containing not onlyhydrocarbon but also hydrogen is coke oven gas. From the PSA or VPSAplant 2 there arises a feed line for the hydrocarbon-rich fraction 3which opens out into a unit for carrying out an oxidation usingtechnically pure oxygen 4. In this unit for carrying out an oxidationusing technically pure oxygen 4, the hydrocarbon-rich fraction ispartially oxidized; that is, the entire amount of substance is notoxidized, but only a part of the amount of substance of thehydrocarbon-rich fraction. Via an introduction line 5 for introducingthe gas stream obtained in the unit for carrying out oxidation usingtechnically pure oxygen 4, this gas stream is introduced as a componentof a reducing gas into the reducing shaft 1. In the partial oxidationthe hydrocarbon content is set in such a manner that the hydrocarboncontent in the reducing gas is less than 12% by volume on entry into thereducing shaft.

The gas stream obtained in the unit for carrying out oxidation usingtechnically pure oxygen 4 is mixed with an auxiliary reducing gas, theresultant mixture is introduced as reducing gas into the reducing shaft1. The two components of the reducing gas are mixed after the auxiliaryreducing gas has been heated in a gas furnace 6. The auxiliary reducinggas is added via an auxiliary reducing gas line 7 for feeding auxiliaryreducing gas to the reducing unit 1, which reducing gas line 7 opens outinto the introduction line 5. Via the introduction line 5, therefore,not only the gas stream obtained in the unit for carrying out oxidationusing technically pure oxygen 4, but also the auxiliary reducing gas isintroduced into the reducing shaft 1, specifically as a mixture termedreducing gas. The temperature preset of the auxiliary reducing gas whichis heated in the gas furnace 6 is set in dependence on a temperaturepreset for the mixture. The gas furnace 6 is arranged in the auxiliaryreducing gas line 7.

From the reducing shaft 1, top gas is conducted away via a top gasoutlet line 8. The auxiliary reducing gas, in the example shown, isformed by mixing dedusted—a gas scrubber 9 is present in the top gasoutlet line 8—top gas that is largely freed from CO₂—a CO₂ removal plant10 is present in the top gas outlet line 8—and a further gas. Thefurther gas is the hydrogen-rich fraction obtained in the separation ofthe coke oven gas.

The gas furnace 6 is operated using a fuel gas. The fuel gas is burntwith feed of air through an air feed line 11 opening out into the gasburner. The fuel gas contains gases of the group

-   tail gas formed in the removal of CO₂ from the top gas,-   top gas,-   coke oven gas,-   hydrogen-rich fraction obtained by separation of coke oven gas.

For feeding these gases into the gas burner 6, there are present

-   a tail gas feed line 12 for feeding tail gas formed in the removal    of CO₂ from the top gas which exits from the CO₂ removal plant 10    and opens out into the gas burner,-   a top gas feed line 13 for feeding top gas which exits from the top    gas outlet line 8 conducting away top gas from the reducing unit and    opens out into the gas burner,-   a coke oven gas feed line 14 for feeding coke oven gas, which exits    from a feed line for coke oven gas 15 and opens out into the top gas    feed line 13,-   a hydrogen fraction feed line 16 which branches off from a hydrogen    fraction outlet line 17 exiting from the PSA or VPSA plant 2 and    opens out into the coke oven gas feed line 14.

In order that auxiliary reducing gas can be obtained by mixing top gasthat is dedusted and largely freed from CO₂ and the hydrogen-richfraction obtained in the separation of the coke oven gas, not only thehydrogen fraction outlet line 17 but also the top gas outlet line 8 openout into the auxiliary reducing gas line 7.

The feed line for coke oven gas 15 exits from a coke oven gas sourcethat is not shown and opens out into the PSA or VPSA plant 2.

In the device shown in FIG. 1, two introduction lines opening out intothe reducing shaft 1 are present. The introduction line 5, called firstintroduction line, has already been described. A further introductionline, called second introduction line 18, branches off from the feedline for the hydrocarbon-rich fraction 3 and opens out into the reducingshaft. Via this second introduction line 18, a subquantity of thehydrocarbon-rich fraction can be introduced directly into the reducingshaft. This subquantity can thus be used for carbonizing the metalliciron, in this case sponge iron, generated in the reducing shaft 1. Acooling gas line for feeding cooling gas into the reducing shaft 1 isnot shown for reasons of clarity; in principle, for the purpose ofcarbonization, a subquantity of the hydrocarbon-rich fraction could alsobe added to the cooling gas via a corresponding branch from the feedline for the hydrocarbon-rich fraction 3 which opens out into thecooling gas line.

In the tar filter appliance 19 arranged in the feed line for coke ovengas 15, tar is removed from the coke oven gas.

In the burner 20, the auxiliary reducing gas can be partially oxidizedwith feed of technically pure oxygen, if this is wanted for temperatureelevation.

For reasons of clarity, depiction of device parts which are notessential has been dispensed with, for example the depiction of diversecompressors, bypass lines, gas holders, gas coolers, flare stacks.

In FIG. 2, in an otherwise similar device and procedure, thehydrocarbon-rich fraction, instead of a partial oxidation, is subjectedto reforming using CO₂ and H₂O before it is introduced as part of areducing gas into a reducing shaft. Plant parts and processes which areidentical to FIG. 1 are not described again here for the most part, andthe reference signs for the same plant parts, for better clarity, arenot entered into the drawing. The reforming takes place in a unit forcarrying out reforming using CO₂ and H₂O, here a reformer 21, into whichthe feed line for the hydrocarbon-rich fraction 3 opens out. Off-gasfrom the reformer 21 is used via a heat exchanger 22 for heating thehydrocarbon-rich fraction before entering into the reformer 21.

Via a plurality of feed lines 23 a, 23 b, which open out into the feedline for the hydrocarbon-rich fraction 3, before entry into the reformer21, a plurality of CO₂-containing gas streams are added to thehydrocarbon-rich fraction. Via feed line 23 a, tail gas from the CO₂removal plant 10 is added; the feed line 23 a arises from the tail gasfeed line 12. Via feed line 23 b, top gas is added. Via a water feedline 24 which opens out into the feed line for the hydrocarbon-richfraction 3, before entry into the reformer 21, steam and/or water isadded to the hydrocarbon-rich fraction.

The reformer 21 can be fired using top gas, coke oven gas or with thehydrocarbon-rich fraction; corresponding lines opening out into thereformer 21, for the sake of clarity, are not shown.

Via a branch line 29 which branches off from the second introductionline 18 and opens out into the first introduction line 5, thehydrocarbon content in the reducing gas on entry into the reducing shaft1 can be influenced via the feed of hydrocarbon-rich fraction.

In FIG. 3, the reducing unit is a fluidized-bed cascade 25, from thelast fluidized-bed reactor 26 of which, seen in the direction of flow ofthe reducing gas, top gas is taken off; the top gas line is given thereference sign 8, as is the top gas line in FIG. 1. The introductionline 5, which in FIG. 1 is shown opening out into the reducing shaft 1,is, in FIG. 3, shown opening out into the first fluidized-bed reactor27, similarly seen in the direction of flow of the reducing gas. As adevice for separating coke oven gas—instead of, as in FIG. 1, a devicefor pressure-swing adsorption—there is a device for membrane separation28. Via a branch from the feed line for the hydrocarbon-rich fraction 3,hydrocarbon-rich fraction can be fed into the first introduction line 5,which offers a possibility for influencing the hydrocarbon content inthe reducing gas.

FIG. 4 differs from FIG. 2 by the same modifications by which FIG. 3differs from FIG. 1. In addition, in FIG. 1, in contrast to FIG. 2, noheat exchanger 22 is present.

A description has been provided with particular reference to preferredembodiments thereof and examples, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the claims which may include the phrase “at least one of A, B and C”as an alternative expression that means one or more of A, B and C may beused, contrary to the holding in Superguide v. DIRECTV, 358 F3d 870, 69USPQ2d 1865 (Fed. Cir. 2004).

1-12. (canceled)
 13. A method for reducing metal oxides using a cokeoven gas, comprising: separating the coke oven gas into a hydrogen-richfraction and a hydrocarbon-rich fraction; subjecting at least asubquantity of the hydrocarbon-rich fraction to at least one operationof the group consisting of oxidation using technically pure oxygen andreforming using CO₂ and H₂O to obtain at least a component of a reducinggas; obtaining an auxiliary reducing gas at least in part by mixing topgas that is dedusted and substantially freed from CO₂, and at least onefurther gas, including the hydrogen-rich fraction produced by saidseparating of the coke oven gas; mixing at least a portion of thecomponent obtained by said subjecting with the auxiliary reducing gas toobtain the reducing gas; and introducing the reducing gas after saidmixing, into a reducing unit containing the metal oxides, where ahydrocarbon content of the reducing gas, as a result of said subjectingand said mixing, is on entry into the reducing unit, less than 12% byvolume.
 14. The method as claimed in claim 13, wherein the hydrocarboncontent of the reducing gas, on entry into the reducing unit, is lessthan 10% by volume.
 15. The method as claimed in claim 14, wherein thehydrocarbon content of the reducing gas, on entry into the reducingunit, is less than 8% by volume, but greater than 1% by volume.
 16. Themethod as claimed in claim 15, wherein the hydrocarbon content of thereducing gas, on entry into the reducing unit, is greater than 2% byvolume.
 17. The method as claimed in claim 16, wherein the hydrocarboncontent of the reducing gas, on entry into the reducing unit, is greaterthan 3% by volume.
 18. The method as claimed in claim 17, wherein saidseparating includes at least one operation of the group consisting ofpressure-swing adsorption and membrane separation.
 19. The method asclaimed in claim 18, further comprising heating the auxiliary reducinggas in a gas furnace prior to said mixing.
 20. The method as claimed inclaim 19, wherein the gas furnace is operated with a fuel gas which atleast in part includes at least one gas of the group consisting of tailgas formed in removal of CO₂ from the top gas, the top gas, the cokeoven gas, the hydrogen-rich fraction obtained by said separating of thecoke oven gas, and the hydrocarbon-rich fraction obtained by saidseparating of the coke oven gas.
 21. The method as claimed in claim 13,wherein the reducing unit is a reducing shaft, wherein said methodfurther comprises introducing a first subquantity of thehydrocarbon-rich fraction directly into the reducing shaft, and whereinsaid subjecting subjects a second subquantity of the hydrocarbon-richfraction to the at least one operation of the group consisting ofoxidation using technically pure oxygen and reforming using CO₂ and H₂O,prior to said mixing.
 22. The method as claimed in claim 21, wherein thehydrocarbon content of the reducing gas, on entry into the reducingunit, is less than 10% by volume
 23. The method as claimed in claim 22,wherein the hydrocarbon content of the reducing gas, on entry into thereducing unit, is less than 8% by volume, but greater than 1% by volume.24. The method as claimed in claim 21, further comprising adding atleast one gas stream containing at least one of CO₂ and H₂O to thehydrocarbon-rich fraction before reforming using CO₂ and H₂O.
 25. Adevice for reducing metal oxides using a coke oven gas, comprising: areducing unit reducing metal oxides; a separating device separating cokeoven gas into a hydrogen-rich fraction and a hydrocarbon-rich fraction;a feed line, connected to the separating device, supplying thehydrocarbon-rich fraction; an operation unit, connected to the feedline, carrying out on at least a subquantity of the hydrocarbon-richfraction an operation of the group consisting of oxidation usingtechnically pure oxygen and reforming using CO₂ and H₂O, to produce anoperation gas stream; at least one introduction line introducing intosaid reducing unit a reducing gas including at least one from the groupconsisting of the hydrocarbon-rich fraction and the operation gas streamproduced by the operation unit; and an auxiliary reducing gas linefeeding an auxiliary reducing gas into at least one of the at least oneintroduction line upstream of the reducing unit, the auxiliary reducinggas including top gas that is dedusted and substantially freed from CO₂and the hydrogen-rich fraction produced by said separating device,whereby the reducing gas and the auxiliary reducing gas introduced intosaid reducing unit by the at least one introduction line having ahydrocarbon content that is less than 12% by volume on entry into saidreducing unit.
 26. The device as claimed in claim 25, wherein thehydrocarbon content of the reducing gas and the auxiliary reducing gas,on entry into said reducing unit, is less than 10% by volume.
 27. Thedevice as claimed in claim 26, wherein the hydrocarbon content of thereducing gas and the auxiliary reducing gas, on entry into said reducingunit, is less than 8% by volume.
 28. The device as claimed in claim 27,wherein the hydrocarbon content of the reducing gas and the auxiliaryreducing gas, on entry into said reducing unit, is greater than 2% byvolume.
 29. The device as claimed in claim 28, wherein the hydrocarboncontent of the reducing gas and the auxiliary reducing gas, on entryinto said reducing unit, is greater than 3% by volume.
 30. The device asclaimed in claim 29, wherein said separating device includes at leastone of a pressure-swing adsorption device and a membrane separationdevice.
 31. The device as claimed in claim 30, further comprising gasfurnace in said auxiliary reducing gas line upstream of saidintroduction line.
 32. The device as claimed in claim 31, wherein saidat least one introduction line includes at least two introduction linesof which at least one is not connected to the auxiliary reducing gasline.
 33. The device as claimed in claim 32, wherein said reducing unitis a reduction shaft.
 34. The device as claimed in claim 32, whereinsaid reducing unit is a fluidized-bed cascade.